Say I was going to rotate a 3D field...like a fighting arena, on its y axis. I know that the matrix for y rotations involves trigonomic functions...but for that to happen, you need a right triangle and a reference angle. My question is: if it's not clearly a triangle...and it's something like a character, or an entire level....how you do determine its reference angle, and the size and location of the triangle?

Originally sine cosine and tangent were considered to be ratios of sides of right triangles, however now they are simply functions of angles.
The formula for the matrix you have rotates a point around the axis (0,1,0) by whatever angle you specify, just transform all the points in your model by the matrix and you should have the rotations you expect.

Quote:Original post by chowe6685
Originally sine cosine and tangent were considered to be ratios of sides of right triangles...

No. That's just how they're introduced. They're circular functions, because they define relationships between two radii and the intervening angle of a unit circle.

Other than that nitpick, chowe6685 is spot on.